1. Field of the invention
This invention relates generally to thermoplastic utility bags and more particularly, to bags fabricated of woven, flat synthetic yarns to produce a light weight, dimensionally stable bag of exceptional strength for heavy duty use as for carrying and dispensing bales of hay.
2. Discussion of the prior art
Thermoplastic shipping bags are an economical means for the packaging, transportation and storage of a wide variety of products in granular, bead, pellet, or powder form. These bags may be either open ended, requiring separate provisions for closing, or fitted with a valved opening. The most commonly used type of thermoplastic bags are manufactured from film made by blown film processes using low density polyethylene and rubber modified high density polyethylene resins and coextruded versions of these resins and allied copolymers. The film may subsequently converted to bags by a variety of sealing techniques. Some of these simple thermoplastic films may be converted to bags by the multiple folding and gluing of the bag ends, but this has the serious disadvantage of requiring very expensive converting equipment, as well as the use of expensive and difficult to control two component glue systems.
Prior art, heat sealed thermoplastic bags are commonly used for the packaging of low cost, non-hazardous products. Their use for higher cost and hazardous products, however, has been badly restricted because of poor puncture and snag resistance of the bags compared with multi-wall paper or woven plastic bags of related composition structures.
Woven plastic bags are shown in U.S. Pat. Nos. 3,439,865 and 3,445,055 to Port et al. The bags are formed by a fabric composed of horizontally-extending flat warp yarns and transversely-extending flat weft or filler yarns. The warp and weft yarns are tightly woven on a textile loom to form a sheet-like material relatively free of interstices. Such yarns may be produced from any suitable synthetic plastic material, including polypropylene, polyamides, such as nylon, polyester or polyacrilic yarns, as well as vinyl and polyethylene. Usable weaves for purposes of their invention lie in the range of 12 .times.12 and lower, and in practice a weave of 3.times.3 is satisfactory. In shaping the fabric into a sack, Port et al cuts a suitable rectangle of the material and folds the same, after which the long end is seamed or heat-sealed to produce a sleeve, and the short end is seamed and possibly reinforced by a marginal fold-over to produce the bottom.
In U.S. Pat. No. 4,576,844, Murray et al disclose a puncture resistant thermoplastic bag of uni-axially oriented polyethylene and inner walls of low density polyethylene, heat-sealed thereto. The film may be subsequently converted to bags by a variety of sealing techniques. Some of these simple thermoplastic films may be converted to bags by sewing but this has the disadvantage of badly weakening the films and introducing unwanted holes in the bag through which moisture or other contaminants can enter or allow environmental contaminants to exit. Other bags may be manufactured by the multiple folding and gluing of the bag ends, but this has serious disadvantage of requiring very expensive converting equipment, as well as the use of expensive and difficult to control two component glue systems. Because of these drawbacks, the use of heat sealing is Murray et al's desired method of manufacture of thermoplastic bags.
I have found however, that properly stitched seams can overcome the disadvantages of the prior art methods of sealing thermoplastic bags. Furthermore, the prior art bags cited above cannot be used for packaging bulky objects such as a bale of hay and any method of heat sealing would be prohibitively expensive. Neither of the patents are concerned with ease of access to the contents of the bags since they are made for a single use and are generally disposable. The bags are formed of a single length of flat material and generally are heat sealed. The patents are generally directed to the construction of the packaging material rather than the assembly for a specific use.